The inverse square law for illuminance is valid for:

When light is incident on a medium at angle $i$ and refracted into a second medium at an angle $r$,the graph of $\sin i$ vs $\sin r$ is as shown in the figure. From this,one can conclude that:

The photograph of a house occupies an area of $1.75 \; cm^2$ on a $35 \; mm$ slide. The slide is projected onto a screen,and the area of the house on the screen is $1.55 \; m^2$. What is the linear magnification of the projector-screen arrangement?

The mirrors are perpendicular to each other as shown in the figure. $A$ light ray $AB$ is incident on the mirror $M_1$. The reflected ray then undergoes a reflection from the mirror $M_2$. The final ray after reflection from $M_2$ will be parallel to the incident ray, if

$A$ container is filled with water $(\mu = 1.33)$ up to a height of $33.25\ cm$. $A$ concave mirror is placed $15\ cm$ above the water level and the image of an object placed at the bottom is formed $25\ cm$ below the water level. The focal length of the mirror is (in $cm$)

Two light sources with equal luminous intensity are placed at a distance of $1.2\, m$ from each other. Where should a screen be placed between them such that the illuminance on one of its faces is four times that on the other face?